H. Päs, und T. Weiler. Phys. Rev., (2001)cite arxiv:hep-ph/0101091
Comment: 24 pages, RevTeX, 4 figures included, slight modification of abstract.
S. Bilenky, C. Giunti, J. Grifols, und E. Masso. Phys. Rept., (2003)cite arxiv:hep-ph/0211462
Comment: 92 pages. Final version to be published in Phys. Rep., with note on
implications of recent WMAP results.